[tip:timers/urgent] tick/broadcast: Handle spurious interrupts gracefully

[tip-bot for Thomas Gleixner <tipbot@zytor.com>]

Commit-ID:  c4288334818c81c946acb23d2319881f58c3d497
Gitweb:     http://git.kernel.org/tip/c4288334818c81c946acb23d2319881f58c3d497
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Sun, 5 Jul 2015 20:53:17 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 7 Jul 2015 18:46:48 +0200

tick/broadcast: Handle spurious interrupts gracefully

Andriy reported that on a virtual machine the warning about negative
expiry time in the clock events programming code triggered:

hpet: hpet0 irq 40 for MSI
hpet: hpet1 irq 41 for MSI
Switching to clocksource hpet
WARNING: at kernel/time/clockevents.c:239

[<ffffffff810ce6eb>] clockevents_program_event+0xdb/0xf0
[<ffffffff810cf211>] tick_handle_periodic_broadcast+0x41/0x50
[<ffffffff81016525>] timer_interrupt+0x15/0x20

When the second hpet is installed as a per cpu timer the broadcast
event is not longer required and stopped, which sets the next_evt of
the broadcast device to KTIME_MAX.

If after that a spurious interrupt happens on the broadcast device,
then the current code blindly handles it and tries to reprogram the
broadcast device afterwards, which adds the period to
next_evt. KTIME_MAX + period results in a negative expiry value
causing the WARN_ON in the clockevents code to trigger.

Add a proper check for the state of the broadcast device into the
interrupt handler and return if the interrupt is spurious.

[ Folded in pointer fix from Sudeep ]

Reported-by: Andriy Gapon <avg@FreeBSD.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20150705205221.802094647@linutronix.de
---
 kernel/time/tick-broadcast.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index c8d731a..ee3cf94 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -316,6 +316,13 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
 	bool bc_local;
 
 	raw_spin_lock(&tick_broadcast_lock);
+
+	/* Handle spurious interrupts gracefully */
+	if (clockevent_state_shutdown(tick_broadcast_device.evtdev)) {
+		raw_spin_unlock(&tick_broadcast_lock);
+		return;
+	}
+
 	bc_local = tick_do_periodic_broadcast();
 
 	if (clockevent_state_oneshot(dev)) {